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Old 6th February 2013, 09:11 PM   #1
diyAudio Member
Join Date: Oct 2012
Question OB - what FR to choose with Tesla woofers

Hi. I've seen fullrange OBs with 15''helpers down there considered a fullrange approach so i hope im in the right sub-forum.

My not so clear question : I'd like to build an OB with a fullrange running 6-8" with a bass driver low-passed 150-200Hz 1st order do match a 2w tube amp. I got a beautiful pair of vintage 14" alnico Tesla ARO835, 4Ohm . But im not sure of FR selection and its impedance / implementation / safety.

id like to run the FR 'undisturbed' so it points to the paralleling the speakers. Does it make sense (quality-wise) ? i want to use its natural bass freq falloff and mate the woofer in that area. but adding a parallel 4Ohm FR would make 2Ohms which seem quite low for the amp.. maybe. Should i search for 8Ohm FRs ? How is it usually done when people use 4ohm helpers with FR-s ? Connecting in series or adding resistors (power loss) are the only solutions ?

thank you

just a snap of new babies on a testing rig
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Old 7th February 2013, 12:07 AM   #2
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Join Date: Nov 2005
Location: NorCal
Unless your amp has a 2 Ohm tap, I'd put them in series.

My OB's use two 8 Ohm, 15 inch drivers wired in series, driven from the 16 Ohm tap of my modified Stereo 70. I couldn't say why, but they sound better than they did in parallel from the 4 Ohm tap. The system is bi-amped, so the imdeance difference between the woofers and full-ranger is not important.

How sensitive are the Teslas?

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Old 7th February 2013, 12:18 AM   #3
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The "obvious" solution that suggests itself is to start with a first order high pass on the 4 or 8 ohm fullrange as well. That allows the load impedance to stay above 4 ohms throughout the band. You already know that your fullrange isn't going to do anything useful below 150 next to those woofers. Somebody well respected once said something like, "It has a capacitor in it. Deal with it".
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Old 7th February 2013, 07:42 AM   #4
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Join Date: Oct 2012
Thanks for reactions.
Primarily, I'd like to know, if i can use a single amp (for low-level, almost nearfield listening) without tradeoffs, and then if series connection of FR and the helper woofer isn't somewhat inferior to the parallel. There seem to be contradictions, i've seen few cases of preferring series, elsewhere something like 'no series please here'. It looks i have to try and listen.

Teslas should be 95db.
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Old 7th February 2013, 10:01 AM   #5
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Join Date: Oct 2012
it should look similar like this
Tiny Alnico Open Baffle

but i'm a bit confused. included crossover pdf looks like parallel to me and in the text is mentioned 'series'. i also dont know the idea behind choosing 16 / 8 ohm. is it related to 2 different versions of both drivers ?
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Old 9th February 2013, 03:17 PM   #6
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Join Date: Oct 2006
Hi Misok...
I am from Martin Slovakia
I have the same alnico driver, but unfortunately only one. Do you know where can I get second one ?

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